Nitration of aromatic ring-containing compositions

ABSTRACT

CERTAIN AROMATIC ORGANIC COMPOSITIONS CONTAINING BENZENOID-SUBSTITUTED HYDROGEN ARE READILY NITRATED BY TREATMENT WITH A MIXTURE COMPRISING A PERFLUORO SATURATED ALIPHATIC ACID ANHYDRIDE OF FROM 4 TO 8 CARBON ATOMS AND A NITRATING AGENT OF EITHER METAL NITRATES OR AMMONIUM NITRATE.

United States Patent C 3,634,520 NITRATION F AROMATIC RING-CONTAINING COMPOSITIONS James V. Crivello, Mechanicsville, N.Y., assignor to General Electric Company No Drawing. Filed Oct. 23, 1969, Ser. No. 868,917 Int. Cl. C07c 43/20, 121/30, 79/10 US. Cl. 260-612 R 7 Claims ABSTRACT OF THE DISCLOSURE Certain aromatic organic compositions containing benzenoid-substituted hydrogen are readily nitrated by treatment with a mixture comprising a perfluoro saturated aliphatic acid anhydride of from 4 to 8 carbon atoms and a nitrating agent of either metal nitrates or ammonium nitrate.

This invention is concerned with a process for nitrating aromatic ring compositions. More particularly, the invention is concerned with a process for nitrating compositions containing aromatic carbocyclic radicals having benzenoid hydrogen thereon, which process comprises treating an aromatic composition selected from the class consisting of aromatic hydrocarbons, halogenated aromatic hydrocarbons (where the halogen can be on the aromatic nucleus or on a hydrocarbon substituent thereof); cyanoaromatic hydrocarbons, carboxy aromatic hydrocarbons, aryloxy and alkoxy aromatic hydrocarbons, halogenated aryloxy and alkoxy aromatic hydrocarbons with a mixture of ingredients comprising a perfluoro saturated aliphatic acid anhydride of from 4 to 8 carbon atoms and a nitrating agent selected from the class consisting of metal nitrates and ammonium nitrate.

The nitration of organic compositions, particularly aromatic compositions, is well known and is an important industrial process for making organic chemicals and compositions which can be synthetic intermediates for a wide variety of other compounds. In the past, a number of nitrating agents have been widely used and have been well described in the literature. Among the reagents which have been employed for nitration of organic compounds include nitric acid, mixtures of nitric acid and sulfuric acid, nitric acid and acetic acid, etc. A recent US. Pat. 3,417,127, issued Dec. 17, 1968, describes the nitration of alkanes, including saturated cycloalkanes, by contacting the alkane hydrocarbon with a mixture of trifiuoroacetic anhydride and nitric acid of a concentration ranging from about 90 to 100 weight percent at a temperature between about to 50 C.

In general the prior art methods for the nitration of simple aromatic compounds have generally been fairly satisfactory. However, when attempts are made to nitrate certain aromatic compositions, particularly organic polymers containing aromatic nuclei in the polymer backbone, one finds that often it is difficult to effect rapid nitration of the aromatic nucleus or to introduce more than one nitro group per aromatic ring; in the case of polymers, it has been found that the usual nitrating agents tended to decompose the polymer under conventional nitrating conditions. Mainly, the decomposition disadvantage manifests itself when employing nitric acid, as in the aforementioned US. 3,417,127, because of the concomitant presence of water when nitric acid is used.

Unexpectedly I have discovered that I am able to nitrate organic compositions of the above class containing aromatic nuclei by employing as the nitrating medium, a mixture of a perfluoro saturated aliphatic acid anhydride of from 4 to 8 carbon atoms and a nitrating agent (hereinafter so designated) selected from the class consisting of metal nitrates and ammonium nitrate.

The advantages of employing this particular set of reactants and conditions are as follows. The procedure for nitrating is basically simple involving readily available starting materials and conventional apparatus. The conditions for nitration are relatively mild and can be used to nitrate compounds which ordinarily decompose when employing the conventional nitrating systems. Furthermore, the nitrating agent employed can be measured out precisely so that control over the reaction is conveniently maintained. Furthermore, once the nitration reaction has been completed, the reaction mixtures are readily worked up since any excess perfluoro anhydride can be readily removed by application of mild heating conditions or even by a low temperature distillation. Additionally, the use of inorganic nitrates involves relatively low cost materials which are readily available in a high state of purity. Furthermore, the anhydride employed can be readily regenerated and be recovered for use again. Finally, the yields which are realized by employment of my nitrating process are, under comparable conditions, generally higher than other nitrating methods, with little or no interfering organic by-product.

I have found that the nitration of compositions containing aromatic nuclei in accordance with my process involves a diiierent type of mechanism than is employed in the nitration of alkanes. Thus, the reaction of aromatic compositions with, for instance, ammonium nitrate and trifluoroacetic anhydride involves a nitronium ion, NO This strongly electrophyllic species reacts with the aromatic ring to generate a sigma-complex which then loses a proton rapidly to form the product in accordance with the following equation as an example:

In contrast to this, the direct nitration, for example, of alkanes with nitric acid and trifiuoroacetic acid involves a free radical nitration in which oxides of nitrogen, such as N0 are the active agents. Generally, oxides of nitrogen or dilute nitric acid are used in such a reaction under rather high temperature conditions causing fragmentation of the carbon skeleton with resultant breaking of CH and CC bonds and their replacement by a nitro group. As a result of the free radical nature of this type of reaction, primary hydrogens are least susceptible to attack while tertiary hydrogens are attacked more easily; and free radical generators such as small amounts of chlorine act as promoters. In this type of system involving the use of nitric acid and trifiuoroacetic acid anhydride, oxides of nitrogen are apparently produced which are responsible for the products observed.

I have found that the presence of a hydroxyl (OH) group on the aromatic nucleus, such as in the case of phenol, results initially in the oxidation to a quinone structure rather than nitration on the ring. The discovery that hydroxyl-substituted aromatic composition can be oxidized in this manner is more particularly disclosed and claimed in my copening application Ser. No. 868,918 filed concurrently herewith and assigned to the same assignee as the present invention. I have additionally found that the presence of a nitro group on the aromatic nucleus seems to inhibit further nitration of that ring. I have further found that an aromatic ring attached directly to an atom of lower valence which is capable of being oxidized to a higher valence, for instance, in the case of triphenyl phosphine, again undergoes an oxidation re- 'to readily isolate and remove from thereaction by nuclear-substituted hydrogen.

Among the perfluorosaturated aliphatic acid anhy drides of from 4 to 8 carbon atoms which may be em-- ployed in thepractice ofthe present invention may be mentioned, for instance, .trifiuoroacetic anhydride (identitied as TFAA), pentafiuoro propionic acid anhydride, septafiuoro butyric acid anhydride, the mixed anhydride pionic acid, etc.

The metallic nitrate (inadditionto the ammonium nitrate) which is employedin the practice of the present invention advantageously has the general formula where M is ametal atom and the valences x and y of the metal and of the nitrate group can be varied depending upon the particular metal employed; accordingly, the number of nitrate groups in the metal nitrate will also -be varied depending on the valence of the metal atom.

Among such metal nitrates which may be employed may 7 be mentioned, for instance, sodium nitrate, potassium nitrate, copper nitrate including the cupric and cuprous forms, cadmium nitrate, lead nitrate, silver nitrate, zir

:onium. nitrate, chromium nitrate, etc. Various metal salts :ontaining varying molecules of water of hydration are included within the term metal nitrate, It .ispreferred that the nitrate employed be either an alkali-metal nitrate their inexpense, ready-availability, purity andtheability mixture, my salts derived from the nitrate. I

The aromatic compounds-which can be nitrated in nany. The aromatic composition may be a simple com pound, or a morecomplex compound containing an aromatic nucleus or aromatic nuclei in which there is present benzenoid unsaturation to which is attached at least one hydrogen which can be the site for the nitrate group.

Among the simple, i.e. non-polymeric aromatic compositions which may be employed in the practice of the Jresent inveniton may be mentioned, for instance, iromatic hydrocarbons (e.g., benzene, naphthalene, mthracene, biphenyl, terphenyl, etc.); aliphatic-sub- ;tituted aromatic hydrocarbons (e.g., toluene, xylene, :thylbenzene, alphamethylnaphthalene, dihexyl benzene, liphenylmethane, 2,2-diphenylpropane, styrene, allyl aenzene, divinyl benzene, etc.); halogenated aromatic hylrocarbons and halogenated aliphatic-substituted aromatic iydrocarbons (e.g., chlorobenzene, dichlorobenze, tetra- :hlorobenzene, trifluorobenzene, dichloronaphthalene, [,4 chlorotoluene, dibromoanthracene, 3,3',5,5-tetra- :hloro-diphenylmethane, a,a-dichloroethylbenzene, etc.; aliphatic ethers of aromatic hydrocarbons, including alkyl lerivatives (e.g., methyl phenyl ether, ethyl phenyl ether, :thyl naphthyl ether, propargyl phenyl ether, allyloxyben- :ene, etc.); cyanoaromatic hydrocarbons (e.g., cyanoben- :ene, terephthaloyl nitrile, etc.); carboxy aromatic hydro- :arbons (e.g., benzoic acid, isophthalic acid, naphthoic lCld, meta-toluic acid, etc.); aryloxy aromatic hydrocarons (e.g., diphenyl ether, phenoxy naphthalene, etc.); ialogenated aliphatic and aromatic ethers of aromatic iydrocarbons (e.g., dichlorodiphenyl oxide, tetrachloroliphenyl oxide, 4-chlorophenoxy methane, etc.) etc.

The ratio of the ingredients employed in my process an be varied widely. Thus, the molar ratio of the periuorinated aliphatic acid anhydride to the metal nitrate or vmmonium nitrate can be between about 25 t0 1 and l to 15. The molar ratio of the ammonium nitrate or the metal obtained from trifluoro acetic acid and pentafiuoro pronitrate to the aromatic compound can also be varied widely and advantageously is between about 15 to 1 and 1 to 15; while the molar ratio of the perfluorinated aliphatic acid anhydride to the aromatic compound is between about to l and 1 0.50. Preferably, the molar ratio of the perfiuorinated acid anhydride tothe ammonium nitrate or the metal nitrate is between about 5 to l and '1 to: 5; the molar ratio of the ammonium nitrate or metal nitrate to the aromatic compound is between'about 3 to l and l to 8; and the molar ratio of the perfluorinated aliphatic acid anhydride to the aromatic compound is between about 1 to 3 and 10 tel. Generally thereshould be present at least 1 mol of the anhydride per mol of the nitrate.

The temperature of the reaction can be also variedwidely butit. has been found that temperatures between about lt) to about 50 C. are more than adequate for the purpose. Generally, ambient or room temperatures are sufiicient thereby permitting operation of the process at temperatures ranging from about 20 to C. without the necessity for applyinga'ny heat. Since the reaction is somewhat exothermic, any additional heat which may be needed for accelerating the reaction can be derived from the exothermic condition which will result- Generally temperatures above to C. may cause the formation of oxidized products, andheat and condensation' reactions leading'to loss :of some of the desired reaction product. I

The reaction is advantageously carriedout in a solvent which is inert to. the reactantsand to the reaction products. Included among such solvents may be mentioned aliphatic hydrocarbons, chlorinated aliphatic hydrocarbo'ns and strongly deactivated aromatic compounds such such as sodium nitrate or ammonium nitrate becauseof I accordance with the practice of the present invention are i as nitrobenzene, benzene sulfonic acid, etc. Specific compositions which may be employed for the purpose include chloroform, methylenechloride, acetonitrile, tetrachloro nitrating effect. The concentration of solvent is not critical and can be varied widely.

In carrying out the reaction, it is generally desirable to add the ammonium or metal nitrate, the aromatic composition, and the perfluorinated aliphatic acid anhydride to the solvent and then to stir the reaction mixture for a period of from a few minutes to about 4 to 5 hours or more until the reaction is completed. The presence of a reflux condenser to take care of the more volatile products formed during the reaction is often desirable. Thereafter, the reaction products are recovered from the reaction mixture by usual means, such as removing the volatile reaction compositions and by-products, as excess perfiuoro aliphatic acid anhydride, any perfiuoro aliphatic acid which may be formed, solvent, and by-products, such as N0 etc. Vacuum or slight heat to elfect fractional distillation is often employed in this instance. Thereafter, the remaining mixture is advantageously mixed with water and the desired product is extracted with a solvent in which the desired reaction product is soluble.

The nitrated compositions obtained in the practice of the present invention have many uses. Many of them can be used as solvents for other organic reactions. Also the nitrated products can be hydrogenated in the presence of hydrogenation catalysts to convert the nitro group to the corresponding amino group. Aromatic compositions containing these amine radicals can be reacted with compositions, such as aldehydes, to form various resinous compositions useful in the molding and insulation art.

In order that those skilled in the art can better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight unless otherwise indicated. In the following examples, the percent yield found for the difierent reactions is calculated on the basis of the inorganic salt used and generally can be related to the following ratio:

Equivalents of nitrated product formed Equivalents of nitrate charged EXAMPLE 1 Percent yield 6 EXAMPLE 3 Employing the same conditions and molar concentrations of the ammonium nitrate and TFAA as in Example 1, but using 0.01 mol of the aromatic compound instead of 0.056 mol benzene, various organic compounds were subjected to the nitration step employing ammonium nitrate and TFAA. The following Table II shows the various aromatic compounds employed, the time of reaction (which varied), and the products and yields of each reaction. In most of the reaction mixtures, the CHCl was omitted. Where CHClg was used (10 ml.), this will be indicated in the table by the presence of an asterisk in front of the Test Number.

reaction mixture became homogeneous. Excess trifluoroacetic anhydride was removed by fractional distillation along with some trifluoroacetic acid (TFA) and CHCl The remaining liquid was poured into 50 ml. distilled water and extracted three times with ml. portions of CHCl There was thus obtained a 95% yield of mononitrobenzene. When the reaction was repeated omitting the TFAA, no detectable nitration occurred.

EXAMPLE 2.

In the following example the effect of nitrating benzene with a variety of nitrating media was explored in order to compare the results with those obtained by using the particular system described in the present application. In each of the tests described below, 5 ml. benzene were nitrated with 0.01 mol (0.8 gram) ammonium nitrate in 70 ml. of CHCl Test No. 1 used 0.035 mol TFAA, While in the other tests, the TFAA was replaced by 0.035 mol of the designated acid or anhydride. The reactions were carried out with stirring for 2 hours at 0., otherwise, the conditions for obtaining the final results were the same as in Example 1. The results of these tests are described in the following Table I.

TABLE I Percent yield nitrobenzene 11 -I. (crgoono l Concentrated (98%) HNO; was substituted for NH4NO in an equimolar amounts, based on the HNO; content.

EXAMPLE 4 In this example, benzene was nitrated in a reaction medium comprising TLFAA and various metallic nitrates. In each instance, the reaction was carried out in the same manner as in Example 1 and the molar concentrations of the benzene and the 'I FAA were the same as in Example 1, except that equivalent molar concentrations of TFAA were used when nitrates having water of hydration were employed. The following Table III shows the various metallic nitrates employed, the time of reaction, and the yield. In each test, CHCl was employed as the solvent in the same concentration as in Example 1.

It will of course be apparent to those skilled in the art that other aromatic compounds containing aromatic groups with benzenoid unsaturation can be nitrated in accordance with the present invention and the nitrating agents such as the metal nitrate and the perfluoro aliphatic acid can vary widely without departing from the scope of the invention. Additionally, the molar concentrations of the aromatic compound, the nitrating agent, and the perfluorinated aliphatic acid anhydride can be varied widely and is not critical as long as there is present a sutficient amount of the perfiuorinated aliphatic acid anhydride to react with either the ammonium or the metal ion to make available the nitronium ion for nitrating purposes.

7 The nitrated compositions of a nonpolymeric nature have many uses including their use as solvents. The nitrated compositions can be reduced to form an aminosubstituted derivative which further renders them reactive either by themselves as solvents or for reaction with other compositions to form derivatives thereof.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In the process for nitrating an aromatic composition containing aromatic carbocyclic radicals having benzenoid 10 hydrogen thereon wherein the aromatic composition is selected from the class consisting of aromatic hydrocarbons, halogenated aromatic hydrocarbons, cyanoaromatic hydrocarbons, carboxyaromatic hydrocarbons, hydrocarbon ethers of aromatic hydrocarbons, and halogenated hydrocarbon ethers of aromatic hydrocarbons, the improvement which comprises treating the aromatic composition with a mixture containing as essential ingredients a per fiuoro-saturated aliphatic acid anhydride of from 4 to 8 carbon atoms and a nitrate selected from the class consisting of metal nitrates and ammonium nitrate.

2. The process as in claim 1 wherein the perfluorosaturated aliphatic acid anhydride is trifluoro acetic anhydride 3. The process as in claim 1 wherein the nitrating agent is ammonium nitrate 4. The process as in claim 1 wherein the perfluorosaturated aliphatic acid anhydride is trifluoro acetic anhydried and the nitrating agent is ammonium nitrate.

5. The process as in claim 1 wherein the aromatic composition is benzene.

6. The process as in claim 1 wherein the aromatic composition is diphenyl oxide.

7. The process as in claim 1 wherein the metallic nitrate is potassium nitrate.

References Cited UNITED STATES PATENTS 3,417,127 12/1968 Smetana 260-466 FOREIGN PATENTS 1,370,376 8/1964 France.

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LELAND A. SEBASTIAN, Primary Examiner US. Cl. X.R.

260-465 R, 515 R, 612 D, 645, 646 

